I was wondering if this is possible:
There are virtual netwoek like lebara, yallo, aldi mobile... and if I'm not mistaken they are using sunrise network. So, if I'd get a phone locked to sunrise, would and let's say aldi mobile card work in it?
Anyone did something similar?

The best thing you can do in terms of 'operator freedom' is to get a dual sim dual standby mobile phone. These can run two Sim cards in parallel and stay connected with two phone numbers. I use a Zopo ZP300+. Ordered directly from the Zopo online shop in China. Really very cool as abroad on vacation I just buy a local Sim card and and tell my phone to use the local Sim card for data transfers. Very cheap ! And finally having affordable mobile data all over the world is very handy. Another worthwile phone would be the UMI X1 as it also (as opposed to many other dual sim phones) manages to transmit on the 900MHz UMTS band.

My case isn't about multi sim phones
Basically I have MVNO card (aldi) and want a new, simple phone, sunrise has some in very good prices but it hard / expensive to unlock them so I asked about above
Interesting thing is that even on aldi mobile website address is.. sunrise
I wonder if aldi is even a MVNO or just brand from sunrise...